A relay valve of this type includes an inlet valve which is formed by a double seat valve which serves as an escape valve and is disclosed in the European catalog of WABCO Westinghouse Fahrzeugbremsen GmbH (catalog page 973 001, February edition 1977). In connection with this known relay valve, the double seat valve exhibits a double valve element having a valve element secured in the housing which forms the inlet valve and having a valve element connected to the control piston which forms the outlet valve.
A relay valve of this type is generally utilized in air brake equipment for vehicles for the quick pressurization and venting of compressed air installations, such as, brake cylinders.
The characteristic curve of such a relay valve is obtained from the relationship of the effective surface of the control piston which is acted upon by control pressure to the effective surface (reaction surface) of the control piston which is responsive to modulated pressure. Accordingly, the maximum outlet pressure was determined either by the maximum control pressure or the maximum value of the inlet working pressure of the relay valve. In the event that a limitation of the modulated working pressure is desired, regardless of the maximum pressure of the control pressure and regardless of the maximum inlet working pressure, the utilization of an additional pressure limiting device in the control line or the working line on either the inlet side or the outlet side is required.